1. Field of the Invention
The present invention relates to an abnormality detection system and method of detecting an abnormality for an idle speed control device of a vehicle.
2. Description of Related Art
Vehicles having idling rotational speed control or “idle speed control” (ISC) are known (for example, see JP-A-Sho 59-46353). ISC adjusts an idling rotational speed by increasing or decreasing an amount of intake air supplied to an engine.
If any abnormality occurs in an ISC device that increases ISC and an intake air amount, the engine rotational speed can become too great. In order to inhibit engine speed from increasing, a control for inhibiting engine speed from increasing can be made together with the ISC.
One method for inhibiting increase of engine speed resulting from ISC abnormality, is to decrease engine speed by reducing supplied fuel, delaying ignition times or combining these methods if the following conditions (1)-(4) are satisfied:
(1) a throttle opening is equal to or less than a predetermined opening;
(2) a vehicle speed is equal to or lower than a predetermined vehicle speed;
(3) an engine speed is equal to or higher than a predetermined rotational speed; and
(4) not under a condition that the supplied fuel is going to be reduced.
Vehicles equipped with an electronic continuously variable transmission (ECVT) in which more precise vehicle speed is required are known. In a vehicle controlled using vehicle speed, a vehicle speed sensor preferably detects a rotational speed of a drive wheel.
However, when a vehicle speed sensor detecting the rotational speed of the drive wheel is used, it is difficult to properly practice the method for inhibiting increase of engine speed resulting from ISC abnormality. This is because if the vehicle speed sensor is just placed to face the drive wheel, vehicle speed is detected even though the vehicle is in a standstill state under an idling condition, such as when the drive wheel is held using a center stand and does not contact the ground.
In view of the above problem, placing a vehicle speed sensor to face a driven wheel and another vehicle speed sensor to face the drive wheel has been considered. Thereby, both control for inhibiting increase of engine speed resulting from ISC and ISC abnormality, and accurate control of the vehicle are practicable.
Another method is to place a vehicle speed sensor for the drive wheel and a center stand sensor detecting that the center stand is in use when the center stand sensor detects use of the center stand, the vehicle speed is determined to be zero even though the vehicle speed sensor placed for the drive wheel detects a vehicle speed. Thereby, the drawback of inhibiting engine speed from increasing resulting from idling of the drive wheel is removed.
However, use of multiple speed sensors or a separate center stand sensor complicate the control and structure of the vehicle.